1. Field of the Invention
The present invention relates to a robot system for conveying an article.
2. Description of Related Art
In a product manufacturing factory or the like, articles may be conveyed from the initial positions to the target positions. When using a robot to convey an article, the article may be lifted up and conveyed by the robot while an end effector of the robot grasps or suctionally holds the article. It is also known in the prior art to provide a conveyance device for conveying an article in a suspended condition.
Japanese Unexamined Patent Publication No. H05-162974 discloses a conveyance device which comprises runner rails, a movable crane unit which includes a liftable hook, a roll grasping mechanism which is suspended by the hook of the crane unit and is used to grasp a mill roll, and a chock rotating mechanism for rotating the chock of the mill roll grasped by the roll grasping mechanism. It is also disclosed in this patent publication that the device further comprises a swinging stop mechanism for preventing the roll grasping mechanism and the chock rotating mechanism from swinging with respect to the crane unit.
When conveying various kinds of articles, among others, a heavy article, for example, one possible method to be employed would be to convey the article in a suspended condition. However, in the case of the conveyance device in which the crane travels on the rails as disclosed in the above patent publication, the direction in which the article is conveyed is limited to the direction along which the rails extend. Furthermore, the conveying speed is slow because the crane travels on the rails. Moreover, one might want to change the orientation of the article during conveyance, but it is difficult to change the orientation of the article during conveyance.
When conveying an article in a suspended condition without using a conveyance device equipped with runner rails, it has been the prior practice to connect a jig to the article and to suspend the article by lifting the jig using a hoist. Then, while keeping the article in the suspended condition, an operator moves the article to the desired position by holding the article by his hand. Then, the article is placed in the desired position by lowering the jig using the hoist. Since the article is moved by hand in this way, the prior practice has had the problem that not it takes time and labor to accomplish the task and safety precautions have to be taken in order to prevent accidents such as dropping the article during conveyance.